Sammendrag
The Norwegian Environment Agency (Miljødirektoratet) tasked NIVA to investigate the presence of microplastics in one of Norway’s largest
freshwater ecosystems, Lake Mjøsa, using monitoring methods which have been recently optimised for the marine environment. Presented here
is a baseline description of microplastic distribution in Lake Mjøsa and Lake Femunden, as well as NIVAs recommendations for future monitoring
of microplastics in the Norwegian freshwater environment. Microplastics were identified in sediment across all sites in Lake Mjøsa. Core slices
from a known volume of sediment are well suited to investigate both geographical and historical distribution of microplastics. Bivalves, such as
the duck mussel appear less useful as a test medium but might be useful for comparative analyses against the marine environment. Samples of
historical plankton could be a useful way to study temporal changes in a specific area. However, fibres need to be excluded from historical samples
as contamination during past sampling campaigns cannot be accounted for. Contamination mitigation measures should be considered in ongoing
plankton sampling to facilitate microplastic monitoring in the future. It is not likely that choosing to investigate only one matrix (i.e. just sediments
or just plankton samples) will provide a robust assessment of microplastic contamination for a whole ecosystem. A combination of water,
sediment and biota samples are recommended. Microplastic monitoring could also be introduced to already established monitoring programs
(e.g. Milfersk and/or ØKOSTOR), albeit gradually, to get a better understanding of microplastic distribution both geographically and between
different matrixes (such as water, sediment and different biota). Long-term, continuous monitoring will eventually generate a knowledge base
for assessing both the fate of microplastics and the effects they may have on organisms.
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